The microquakes just north of Yellowstone Lake calmed down yesterday, after a period of apparent tremor in the afternoon. Traces are quiet early this morning. Yellowstone remains a faint, remote threat, so far as any world-changing event is concerned. A hydrothermal blast blowing out the highway and gouging a new bay of the lake would make plenty of headlines, but such explosions have occurred in the recent geological past, without further eruptive activity. There is no basis to believe that current, minor uplift portends any dangerous inflation of the magma chamber.

Chaitén Volcano is another matter. When the weather cleared yesterday afternoon. the mountain gave a fine show of fuming and ash ejection. The rate of dome growth remains extremely high — the immense pile enlarges visibly from week to week. If this trend continues, the dome will be soon spalling hot avalanches outside the buried caldera and into the valley that leads toward Chaitén town.

As the months of this unprecedented pileup pass, I get an uneasy feeling that the outcome of this process will not be a new mountain, thousands of feet higher than the old caldera rim, but a new caldera of much greater size. The mass of dome material must now amount to many cubic kilometers, and who knows how much more might emerge in a caldera-forming blowout. We could be talking of a Tambora sized event — or worse.

With the sun in a funk and global climate already cooling, such a sharp volcanic nudge would precipitate global food crisis and potential world war for control of vital resources. This scenario has worried me from the day that Chaitén began erupting. It was clear that we were witnessing an event outside the parameters of ordinary volcanic activity. That does not necessarily mean a disastrous climax will come. It simply means that the course of the eruption is uncommonly unpredictable. We can only watch and wait.